The Java Language Specification, Third Edition

CLASSES Constructor Modifiers 8.8.3
8.8.2 Constructor Signature
It is a compile-time error to declare two constructors with override-equivalent
(§8.4.2) signatures in a class. It is a compile-time error to declare two constructors
whose signature has the same erasure (§4.6) in a class.
8.8.3 Constructor Modifiers
ConstructorModifiers:
ConstructorModifier
ConstructorModifiers ConstructorModifier
ConstructorModifier: one of
Annotation public protected private
The access modifiers public, protected, and private are discussed in
§6.6. A compile-time error occurs if the same modifier appears more than once in
a constructor declaration, or if a constructor declaration has more than one of the
access modifiers public, protected, and private.
If no access modifier is specified for the constructor of a normal class, the
constructor has default access. If no access modifier is specified for the constructor
of an enum type, the constructor is private. It is a compile-time error if the
constructor of an enum type (§8.9) is declared public or protected.
If an annotation a on a constructor corresponds to an annotation type T, and T
has a (meta-)annotation m that corresponds to annotation.Target, then m must
have an element whose value is annotation.ElementType.CONSTRUCTOR, ora
compile-time error occurs. Annotations are further discussed in §9.7.
Unlike methods, a constructor cannot be abstract, static, final, native,
strictfp,orsynchronized. A constructor is not inherited, so there is no need to
declare it final and an abstract constructor could never be implemented. A
constructor is always invoked with respect to an object, so it makes no sense for a
constructor to be static. There is no practical need for a constructor to be synchronized,
because it would lock the object under construction, which is normally
not made available to other threads until all constructors for the object have
completed their work. The lack of native constructors is an arbitrary language
design choice that makes it easy for an implementation of the Java virtual machine
to verify that superclass constructors are always properly invoked during object
creation.
Note that a ConstructorModifier cannot be declared strictfp. This difference
in the definitions for ConstructorModifier and MethodModifier (§8.4.3) is an
intentional language design choice; it effectively ensures that a constructor is FPstrict
(§15.4) if and only if its class is FP-strict.
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